1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to a turbine stator vane with endwall leading edge corner cooling.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A gas turbine engine, such as an industrial gas turbine (IGT) engine, includes one or more rows of stator vanes that react with a hot gas stream to redirect the stream into an adjacent row of rotor blades. The first stage stator vanes are exposed to the highest temperatures, and therefore require the most amount of cooling.
FIG. 1 shows a side view of a stator vane with a bow wave effect in front of the vane. A bow wave driven hot gas flow ingestion is created when the hot gas core flow 10 enters the vane row and the leading edge of the vane induces a local blockage which creates a circumferential pressure variation at the intersection of the airfoil leading edge location. The leading edge of the vane generates upstream pressure variations which can lead to hot gas ingress 11 into the front portion of the mate-face gap. If proper cooling or design measures are not undertaken to prevent this hot gas ingress, the hot gas ingress can lead to severe damage to the front edges of the vane endwalls as well as to the sealing material or mate-face in-between vane endwalls.
As seen in FIG. 1, this bow wave effect appears ahead of the turbine vanes. The high pressure ahead of the vane leading edge is greater than the pressure inside of a cavity or gap formed between adjacent vane mate-faces. This leads to a radially inward flow of the hot gas into the cavity. The ingested hot gas flows through the gap circumferentially inside the cavity and towards the lower pressure zones. The ingested hot gas then flows out at the points where the cavity pressure is higher than the local hot gas pressure. FIG. 2 shows a top view of a pair of vanes where the hot gas ingestion flows into the vane mate-face gap. the bow wave effect forces the much of the hot gas stream off of the leading edge of the vane and downward and into the gap of the adjacent vane mate-face along the suction side of the vane endwall and causes the most damage. FIG. 3 shows areas of distress for a vane leading edge corner where cooling is needed to address this hot gas ingression issue. TBC spallation 14, cracking 15 and erosion of the honeycomb 16 below the endwall are indicated in this figure.
In general, the size of the bow wave is a strong function of the vane leading edge diameter and distance of the vane leading edge to the endwall edge. Since the pressure variation in the tangential direction with the gap is sinusoidal, the amount of hot gas flow penetrating the axial gap increases linearly with the increasing axial gap width. Thus, it is important to reduce the axial gap width to the minimum allowable by tolerance limits in order to reduce the hot gas ingress.